Kurt bobber



K. BOEBER. TRANSFORMER.

APPLICATION FILED NOV 31 I914- HENEWED JAN. 21, 1919.

1 y 1 1 w Patented Sept. 9, 1919.

TED STATES PAT NT. OFFIC KURT ROEBER, or HALLE-omTHmsnALE, ERMANY.

TRANSFOR R.

ApplicationfiledNovember a, 1914, sari-.11 nolis'iaoei. Ren wed Janiiiary e1, 19 19. serial n6. 27 1.34

To all whom j Be it known that I, KURT Ronenma Ger; man citizen, and resident of Halle on-the- Saale, Germany, have invented certain new and useful Improvements in Transformers, of which the following is a specification.

My invention relates to 'so-called measuring instrument transformers, which are used for instance inalternatlngcurrent central stations for. thepurpose of avoidingthe use ofhigh tensions or large currents di-- rectly in measuring instruments; my invention refers in particular to so-called current transformers which are used for the above named .purpose in connectionwith ammeters or with the current coils of watt meters or the like. i y y In order to be theoretically perfect, such instrument transformers must fulfil two conditions which "do not exist in case of power transformers; v1. The phase I primary and the secondary terminal potential in case of voltage transformers, and the phase displacement between the primary and the secondary current in case of current transformers, should be exactly 180 at all practically possible load values of the transformer. y

2.The relation of the primary and? secondary .potential or current should remain the'jsafne for all practical load values of the transformer. H y I a Y In the light of these conditions the instrument transformers constructed heretofore are rather imperfect. As may be known to those skilled in the art, they can be im proved already to a considerable extent when they are connected with a condenser for compensating the no-l0ad current.

In the present inventlon a general 1mprovement of these transformers is obtained principally by making the phase displace ment between the primary and the secondary potential or current independent to a larger ;ing the problem to be solved by my invention;

displacement between the mentioned here only incidentally.

Ishall; explain the character of my invention taking a current transformer as an example and it may be presumed that the secondary terminals of 'the transformer are permanently connectedwith the same noninductive or inductiveload resistance.

My inventlonj s illustratedin the accompanying drawings in which:

Figure l is a diagram used for explain Fig. 2 is a diagram for explaining the fundamental theoretical idea underlying my invention; i y

Fig. '3 is a wiring diagram of a preferred practical form and Fig. 4 is .a.,detail of a particular mechanical feature of the apparatus constructed according to my invention.

It is well known that in transformers of the character referred to, the relation and the phase displacement between theprimary and secondary current is influenced by the no-loadcurrent, that isto say influenced by the component of the primary current which is necessary for producing the} magnetic field inthe iron core of" the transformer. This n0-load current is again usually considered as a resultant of two components, a". e., thefwattdess component" or magnetizing component, which represents the pure .specificationlof ietters f'atenth Patented y magnetizing current of the iron, and the watt component which represents the current used for cover ng the iron losses through hysteresisfand eddy currents. If the well known vector-diagramis plotted indicating for the several load values that, is to say, for

the several values of the current, in the secondary transformer-I circuit closed as presumed above, the corresponding values of the watt-less component and of the Fwatt compdnentiofthe no-load current together withtheir relative phase displacement and the displacement over' the secondarycnrrent, and if from the components of the no-load current and of a current equalto the secondary current but displaced 180, the primary current is defined as a resultant in usual manner, it is found that the phase displacement be tween the primary current and the secondary force.

current of the transformer varies with the varying secondary current because the mag- :netizing component of the no-load current does not vary proportionately to the secondary current of the transformer. The reasonfor this is found in the varying permeability reason, it is not proportional to the secondary'current which is generated in the secondary circuit by the induced electro-motive The difl'erences in the proportion between the magnetizing component and the electro-motive force which alone I shall hereinafter use as comparative values, compared with the exact proportionality, are according to experiments with current transformers of such character that when the electro-motive force rises from zero to'a value corresponding with maximum load, the magnetizing component increases slower than the electro-motive force, because the magnetic conditions of the transformeriron which exist in this case arerepresented by points in the magnetizing curve which are located below the point of maximum permeability.

' Through my invention I obtain a better ratio between the magnetizing component of theno-load current on one hand and the induced electro-motive force and thus the secondary current on the other hand. .I gain this advantage by adding to the actual no-load current of the transformer to which reference was made heretofore, a current which I shall call hereinafter additional no-load current, so that from the actual noload current and theadditional no-load current, a new no-load current results which I shall call total no-load current. The additional current is proportioned so that its magnetizing component grows faster than the inducted electro-motive force. Thus the magnetizing component of the totalno-load current will then become more proportionate to the induced electro-motlve force, because the faster increase of the new compo- -nent compensates the too slow increase of the actual magnetizing component. 7

It can be easlly seen that a transformer having a total no-load current as described above, can be corrected quite perfectly through the connection with a condenser to compensate the total no-load current, whereby this condenser may be for instance in parallel to-the load resistance and be connected at the terminals of the secondary winding or it may connected to a separate secondary winding. The reason for this good compensation is that the current which occurs in the primary winding of the of which the transformer'core is made.

transformer, owing to the connection with the condenser, is proportionate to the induced electro-motive force and, as is known, has a phase displacement of 180 against the magnetizing component of the no-load current, and its compensating effect on the no-load current, strictly speaking, consists in compensating the magnetizing component of the no-load current. Thus in case of a transformer whose total no-load current has a magnetizin component proportionate to the induced e ectro-motive force, this compensation is substantially perfect, whereas in an ordinary transformer it can only be imperfect.

In order to illustrate these fundamental theoretical principles of my invention, I have plotted in the coordinate system in Fig. l. of the drawings, the curve C, which represents the relation between the magnetizing component of the actual no-load current and the induced E. M. F. of a current transformer wherein the several values of the induced E. M. F. (E) are taken as ordinates and the corresponding values of the magnetizing component (I...) of the actual no-load current are taken as abscissae from O to the right side of the abscissze axis. The curve C, in its character is the lower portion of the magnetizing curve of the il'iOlIll,

e point C" of the curve having the abscissa I" and the ordinate B may correspond with the full load of the transformer. In the same coordinate system I have represented the relation between the induced E.

-M. F. and the capacity current (I by the values have in a vector diagram having vectors rotating in the sense of the arrow. Thus the lines 0' L 0 E, 0 I 0 I O E", 0 I may also be considered as vectors. Now I have chosen the current intensity I equal to the current intensity I,,,. Owing to thisselection the compensation of the magnetizing component of the actual noload current in case of full load, is in the transformer in question perfect at the value E of the induced E. M. F., in all other cases imperfect, because the'portion ri of the magnetizing component I between the curve C, and the straight line 0 C" represented especially by the curve C,, remains uncompensated. In Fig. 2, I have illustrated the underlyingtheoretical idea of my invention. Aside from the curve C,,I have plotted the curve C havingthe abscissa 1m and the ordinate E," which represents the relation between the magnetizingcompog nent of the additional no-load current and the induced E. M. FQwhich isinecessaryfor the complete compensation of the magnetizing component of the total no-load current by means of acondenser. of curve C, when added tothe abscissa I...

of curve '0 results in the abscissa of a straight line G which thus representswa linear relation between the magnetizing component of the total no-load current and the induced E. M. F. Now for theperfect compensation of-this magnetizing component, a condenser is necessary and sufficient which at full load of the transfonner,i: 6.,

at the value E of the induced E. M. F., produces in the primar winding of the transformer a capacityic is J :J This oapacit E. M. F. by the straight line C, in Fig; 2.

magnetizing iron core so that it is magnetized by the our- 7 rentin a secondary winding of the current transformer and I make this iron corefof such dimensions and of such .materlalt-hat when the load of the current transformer is increased, the state of highest permeab lity: has passed already at small values of this load, at any rate before the maximumload is reached and so that at the higher load values of the transformer the condition of "1 then connect coil (Z containing the auXil-Q saturation is approached. In order to magnetize the core with the aid of a secondary current of the current transformer, I place it within a coil or winding d, Fig. 3, having its ends connected with the endsfof asec-,

ondary coil or windingofthe current transformer. I may use for this purpose either the same secondary'coil or winding Off/he transformer, to which the load resistance is connected as, for instance, coil 'S, Fig. 3;and

iary core to the terminals of said secondary coil or winding Sof the transformer. This modification is so obvious that I have omitted the illustration thereof. I may, how ever, also use a special secondary winding on the current transformer for this purpose.

This modification is shown in Fig. 3 at 0.

plural secondary windings with refercnce to the current or mstru ment transformer I mean to imply any suitable number of secondary windings, whether they" be connected with the load resistance or whether they be separate windings arranged solely for the purpose of feeding coil d, and

plainedhereina The abscissa tfwhoseyalue rent is represented in its dependency from thejinduced qvery large inductance thus it carries the currentwh ch lags lnflphas'e overqthe secthis plural I mean to cover both forms offconnection, referred to above, as equiva lents.i If condenser is used at thesame time in 'order to compensate the total no loadcurrent, Ifpreferyfor reasons to be exter, to connect the condenser to a secondary winding on the iron'core so that the condenser is supplied from the currenttransformer, or asit will be termed hereinafter the 1naintransformer by way of an additional or auxiliary transformer.

This modification ofmy invention is illus- 1 trated diagrammatically in Fig, 3. Inthis rfigure iafrepresents the iron core of the main transformer, 31 itsprin'iary, 8 its secondary winding, the lattersbeing connected in circuit with a measuring instrument m as aload res1stance. c s another secondarywlndingof themain transformer. Itis connected wlth the primary winding of the i. auxiliary transformer whose iron core and secondary winding is representedat b and c respeo tively. In circuit with secondary winding .2

is the eondenser la. In orderto understandv thatcoil dwith its iron core I) has the effect upon the main transformer described above, it is-first presumed thatthe condenser 71 isfremoved. In case coil cof the main transformer is {then merely loaded with a ondaryE. MLF. of the maintransfonnerat an angle approaching 1'close1y and thus a current is produced latheprimary wind.

fing p of the main transformer'whose phase is approximatelythe same as the"phase of the actual no-load current of the main transf-former. [This current is called additional no-load current because it also occurs in the primary coil of the main transformer when thecircuit-of thesecondary coil 0 of the main transformer isop'en.

.If now the condenser is is connected to the secondary coile of gthe auxiliary trans-l former, coil 0 ofthe main transformeris loaded with a resistance of particular char-= fact/er. In this case in the coil oaside from Qthe current forproducin the field in the (iron core 6 of the auxi iary transformer, also the capacity current flows which occurs "in: the primary coil d o-fthe auxiliary trans formenowing to. this condenser connection. om-vac, in theme, assumed in Fig. 2 gives anidea oftlie relation between the value of -this mixed load currentof coil 0 and the E. M. F. induced in this coil. The abscissa.

of the abscissaeJ and j However. curve 2'. of this curve is equal to the algebraic sum Iherefore when using in the clalms the V regarded, but also the ohmic and inductive dropin potential in the coils 0, d and 6. Now I have found that these drops in potential influenced the characterof curve C and that it is possible by affecting these potential drops, especially the inductive one, to conform curve C closely to C For this purpose I propose for instance to produce an viding a special iron core excited by coil (2 artificial stray flax forthe primary coil 0! of the auxiliary transformer by placing the secondary coil 6 only on one ofthe two parallel portions of the iron core I) or by proalone. By suitably dimensioning the stray path it may be brought about that the iron in the stray path-is not .yet saturated at the maximum values of the E. M. F. aflecting coil 03; or it may be also brought about that -it is alread saturated at the smallest values of this E. F. it may also be brought about that it commences to be saturated at a me dium value of theE. M. F. According towhich of the three conditions exists the curvature of curve (3 in Fig. 2 is greater or smaller, or the curvature may be smaller in its lower portion and greater in its upper 7 portion.

I have now'explained the general points on which my invention is based and according to which it may be reduced to practice.

In 7. detail the dimensions of the coils and iron cores which are necessary for the con-- struction according to my invention, must be ascertained by calculation or experiment accordingto the'particular type of instrunient'transformer to be used, 1

The possibility already mentioned of utilizing the potential drops in the coils d, e, of

the auxiliary transformer accordirg to Fig. 3 for affecting'the form of curve. 7 in Fig.

2, and to thus obtain as perfect an effect as possible, is one of the reasons which has prompted me to prefer the modification shown in;Fig.3 of the drawings. A second and very important reason for usingthis form is that in this case, the condenser is protected from too high a potential and it may therefore be made quite small and be cheap to build. This has the following reasons If, through some cause the circuit of the'load reslstance is interrupted, the field 1n the iron core of the main transformer assumesvery'high values whereas the demaga netizing effect of the secondary winding is not present in that case. Consequently, the

E. M. F. effective in the circuit of the prismall cross sections.

mary coil (5 of the auxiliary transformer increases far beyond the values which it can assume in-case of normal operation and it is immaterial in this case whether the coil d 1s connected to a special secondary coil 0 or'connected to the secondary coil d of the main transformer in parallel to the load resistance. Now the field in the iron core of the auxiliary transformer cannot increase in the same measure because this iron core is already saturated at small values of the E. M. F. of the main transformer which occur under normal conditions. Consequently, the condenser is, even if the load resistance should be cut off at the full primary current of the main transformer, would not be subject to an appreciably higher potential than exists under normal conditions at full load of the main transformer with the load resistance connected.

The iron cores necessary for the construction according to my invention have very I therefore prefer to form these. cores by bending sheet iron strips into circular or rectangular shape and by joining their ends. In order to get as good magnetic connection of the ends as possible, they may be electrically welded together. This form is shown in Fig. 4 of the drawings. In this modification (Z represents the primary coil, 6 the secondary coil of the auxiliary transformer whose iron core is b which is common to the primary. and secondary coil; f is an iron core which is energized by the primary coil alone, in order to increase the stray flux 'of this coil. The iron cores 6 and f are bent together from sheet iron strips with their ends welded together as shown at B and F. I should mention that the underlying principles of my invention described with respect to a current transformer as an example, may also be applied in case of a voltage transformer. However, the importance of my invention is Y not as great for voltage transformers as for current transformers, because the range withinwhich the potential varies from its normal value, is small compared with this normal value, so that also the magnetic flux density in the iron core of the transformer and with it the permeability of the iron is changed only. little, and further because the influence of the magnetizing component of the no-load current becomes effective only at the primary potential drops which themselves constitute only a small fraction of the primary potential.

I have at the beginning stated the decrease of the effect of thctransformer load on the phase displacement between the primary and the secondary current or voltage as one of the chief features and advantages of my invention. However, great benefit may be derived from my invention also by permitting the usual variation in phase displacenausea ment, common tothe ordinary instrument transformersfialso to exist in 'my case, but by making the instrument transfonner itself on the other hand, smaller and thus cheaper. This is permissible because when employing the features according to my invention higher values of the magnetic flux density a in the iron core of the transformer are permissible, which; values are located in the range of the magnetizing curve in which the permeability strongly increases with the field intensity. Lastly through my invention the instrument transformer is improved as well asits-manufacture cheapened.

I claim l. The combination with an instrument transformer havin "an ron core, a primary winding and secon ary windings thereon, of,

an auxiliary iron core carrying suitable windings connected to some of the secondary windings ofthe instrument transformer to magnetize said auxiliary core and having such dimensionsand being constructed maximum permeability before the maximum of such material that the iron transgresses the state of maximum permeability before the maximum load of the instrument trans former is reachedwhen its load is increased.

2.. The combination with a current transformer having an iron core, a primary wind-i mg and secondary windings thereon, of an auxiliary transformer ,having a primary winding connected to one of the secondary windings of the current transformer and also having itself a secondary winding and 'a condenser in circuit therewith and having a an II'OIl core of such dimensions and material, that its iron transgresses the state of load of the current transformer isi reached former having an iron core and a primary when its load is increased, 3. The combmatlon with a current trans- Witnesses:

- winding and secondary windings thereon, of

an auxiliary transformerhaving aprimary wlndmgi connected to one of the secondary win-dings of the current transformer, and

having itself a secondary Winding having itself a condenser in circuit wlth t, sald auxillary transformer havmg an lron core of such dimensionsland such material that the iron transgresses the state oft maximum permeability beforethe maximum load of the current transformer is reached when the load is increased and magnetic means 0peratively connected with the primary coil of the auxiliary transformer for increasing the stray flux of said coil.

4; The combination with a current transformerhaying an iron core and thereon a primary and one secondary wmdmg "connected to a load resistance and havmg a second separate secondary winding, of an auxiliary transformer having a primary winding connected to said separate secondary Windingof .the current transformer, asec ondary winding on the auxiliary transformer having a condenser in circuit with it, said auxiliary transformer havingan iron core of such dimensionsand of such material that i the iron transgresses the state of maximum -permeability before the maximum load of the current transformer is reached When the load is increased, and an iron core operatively connected with the primarywinding of the auxiliary transformer for increasing the stray flux of this winding.

In witness whereof I have hereunto set my signature in the presence of two sub scribing witnesses.

" KURT ROEBER.

'RUDOLPH Fnicxn, Anion DUNGER. 

